Technical Field
The present disclosure relates to a semiconductor integrated device, for acoustic applications, with a contamination protection element, and to the manufacturing method thereof. In particular, the semiconductor integrated device includes a MEMS acoustic transducer, and the contamination protection element is a filter adapted to protect the MEMS acoustic transducer from dust.
Description of the Related Art
In a known way, an acoustic transducer (in particular a microphone) of the MEMS (Micro-Electro-Mechanical System) type comprises a membrane sensitive structure designed to transduce acoustic-pressure waves into an electrical quantity (for example, a capacitive variation), and reading electronics designed to carry out appropriate processing operations (amongst which amplification and filtering operations) on said electrical quantity for supplying an electrical output signal (for example, a voltage) representing the acoustic-pressure wave received. In the case where a capacitive detection principle is adopted, the microelectromechanical sensitive structure in general comprises a mobile electrode, obtained as diaphragm or membrane, set facing a fixed electrode, for providing the plates of a variable-capacitance detection capacitor. The mobile electrode is anchored by a first, generally perimetral, portion thereof to a structural layer, whereas a second portion thereof, which is generally central, is free to move or bend in response to the pressure exerted by the incident acoustic-pressure waves. The mobile electrode and the fixed electrode thus provide a capacitor, and bending of the membrane that constitutes the mobile electrode causes a variation of capacitance, as a function of the acoustic signal to be detected.
With reference to FIG. 1, an acoustic-transducer device 19 is represented. The acoustic-transducer device 19 comprises a first die 21 that integrates a MEMS structure 1 provided with a membrane 2, mobile and of conductive material, which faces a rigid plate 3 (whereby is meant an element that is relatively rigid with respect to the membrane 2, which is, instead, flexible). The rigid plate 3 includes at least one conductive layer facing the membrane 2 so that the membrane 2 and the rigid plate 3 form facing plates of a capacitor.
The membrane 2, which in use undergoes deformation in response to incident acoustic-pressure waves, is at least partially suspended over a structural layer 5 and directly faces a cavity 6, obtained by forming a trench in a rear surface 5b of the structural layer 5 (the rear portion 5b is opposite to a front surface 5a of the same structural layer 5, set in the proximity of the membrane 2).
The MEMS structure 1 is housed in an internal cavity 8 of a package 20, together with a further die 22, of semiconductor material, which integrates a processing circuit, or ASIC (Application-Specific Integrated Circuit) 22′. The ASIC 22′ is electrically coupled to the MEMS structure 1 by an electrical conductor 25′, which connects respective pads 26′ of the first and second dice 21, 22. The first and second dice 21, 22 are coupled side by side on a substrate 23 of the package 20. The first die 21 is coupled to the substrate 23 at the rear surface 5b of the structural layer 5, for example by an adhesive layer. Likewise, also the second die 22 is coupled to the substrate 23 at a rear surface 22b thereof. The ASIC 22′ is provided on a front surface 22a of the second die 22, opposite to the rear surface 22b. 
Appropriate metallization layers and vias (not shown in detail) are provided in the substrate 23 for routing the electrical signals onto the outside of the package 20. Further electrical connections 25″, obtained with the wire-bonding technique, are provided between pads 26″ of the second die 22 and respective pads 26″ of the substrate 23.
Further coupled to the substrate 23 is a covering 27 of the package 20, which encloses the first and second dice 21, 22. Said covering 27 may be of metal or pre-molded plastic.
Electrical-connection elements 29, for example in the form of conductive lands, are provided at the underside of the substrate 23 (the side exposed outwards), for soldering and electrical connection to a printed-circuit board.
The substrate 23 further has a through opening, or hole, 28, which sets in fluid communication the cavity 6 of the first die 21 with the environment external to the package 20. The through opening 28 (in what follows referred to as “sound port”) enables introduction of a flow of air from outside the package 20 and of the acoustic-pressure waves, which, impinging upon the membrane 2, deflect it.
In a known way, the sensitivity of the acoustic transducer depends upon the mechanical characteristics of the membrane 2 of the MEMS structure 1, and further upon the assembly of the membrane 2 and of the rigid plate 3. Further, the volume of the acoustic chamber formed by the cavity 6 directly affects the acoustic performance, determining the resonance frequency of the acoustic transducer.
Thus, multiple constraints are imposed on assembly of a MEMS acoustic transducer, which render design thereof particularly problematical, in particular where extremely compact dimensions are desired, as, for example, in the case of portable applications.
In order to protect the cavity 6 and the membrane 2 at least partially from dust and/or water and/or other debris that might penetrate through the through opening 28 thus reducing the useful dimensions of the cavity 6, and thus jeopardizing the performance of the acoustic transducer, it is known to provide a filter (illustrated only schematically in FIG. 1, and designated by the reference 30) outside the package 20 and facing the sound port 28 (at a distance therefrom). This filter 30 is, for example, coupled to a protective shell of a portable device (e.g., a cellphone) that houses the package 20.
In particular, in the case of portable applications, the package 20 is housed inside the protective shell of the portable device itself in such a way that the sound port 28 in turn faces a respective through opening, or hole, made through the protective shell of the portable device by interposition of the filter 30 itself. The filters currently used are mounted manually on the protective shell of the portable device and consequently present excessive dimensions with respect to the actual operating need, which is to protect exclusively the cavity 6, in addition, obviously, to the membrane 2 and the rigid plate 3.
Further, the filter 30 prevents entry of contaminating particles through the hole made through the protective shell of the portable device, but does not solve the problem of contamination deriving from particles of dust or other debris coming from various sources (for example, on account of a not perfectly hermetic closing of the protective shell). In particular, filters of the known type are altogether ineffective in regard to protection from contaminating agents during intermediate manufacturing and assembly steps, i.e., during steps of assembly of the package in the portable device.